Quantifying the amount of impact ejecta at the MER landing sites and potential paleolakes in the southern Martian highlands

Abstract

Applying previous equations for estimating ejecta thickness to Mars, tens of meters of ballistically-emplaced impact ejecta might be expected over the heavily-cratered southern Martian hemisphere. The calculated thickness of ejecta material, even accounting for large uncertainties in methods of estimation, is not enough to fully explain observed depth discrepancies in Gusev Crater or in other potential Martian paleolakes. Ejecta contributed to the Spirit landing site in Gusev Crater is largely derived from local craters while distal ejecta from large, faraway craters dominates the contribution to the Opportunity landing site in Meridiani Planum. However, emplacement of this type of ejecta probably predates the present surfaces. Thira crater may have excavated impact-melt products created by Gusev, samples of which would provide a unique insight into the composition of the bulk Martian crust. Though ballistically-emplaced crater ejecta contribute a relatively small amount of material to any given site, this type of material provides important lithologic diversity. Copyright 2006 by the American Geophysical Union.